The human immunodeficiency virus (HIV), which is the etiological agent of AIDS, is a serious public health threat in the United States and throughout the world. HIV encodes several regulatory proteins not found in simpler retroviruses. One of these, the tat protein, activates gene expression and is essential for viral replication. We propose to study structure/activity relationships of the tat protein and to try designing compounds that will inactivate tat and block replication of HIV. The first goal is to critically test our proposals, based on preliminary experiments, that 1) the tat protein forms a metal-linked dimer in vivo and that 2) cellular uptake of tat may activate latently infected cells. Later studies will focus on the detailed mechanism of tat uptake and the effects of different metals and chelators on tat activity. We have developed a simple tissue culture assay for tat and will use this assay to measure the activity of synthetic peptides and proteolytic fragments, to determine which regions of tat are required for cellular uptake and gene activation. These biochemical studies should help us develop initial strategies for inactivating tat, and possible inhibitors can be screened very rapidly with our tissue culture assay. However, to develop a solid basis for rational drug design, we also will try to crystallize tat and will collaborate with Dr. Gerhard Wagner's laboratory on 2D NMR studies of tat.